How to Measure Correctness in a Web Site?

Back in the day, you were supposed to put all your java script in the head and in the head section of your web sit. At some point they told you to stop doing that, because that would block the of the page. And this is like why they say tracking the client side latency actually matters. In the old days, with those scripts being up in the head, it might be three seconds before your page would render - even though it had the content for the rest of the body.